THE ELECTRONIC SPECTROSCOPY OF THE AMINO-ACIDS TYROSINE AND PHENYLALANINE IN A SUPERSONIC JET

The electronic spectra of the amino acids tyrosine and phenylalanine have been measured in a supersonic jet using laser-induced fluorescence spectroscopy. Through power-dependent studies we have shown that tyrosine and phenylalanine have multiple conformers, and we have assigned spectral features produced by the individual conformers. Dispersed emission spectra of the conformers following excitation of their respective electronic origins reveal that the major vibrational activity occurring in tyrosine and phenylalanine originates from the ring vibrational modes of their respective chromophores. In contrast with previous tryptophan studies, no evidence of intramolecular exciplex formation was observed in any of the tyrosine and phenylalanine dispersed emission spectra. The lack of broad, red-shifted emission characteristic of intramolecular exciplex formation was attributed to the large energy difference between the 1La and 1Lb states. © 1992.